The present invention relates to a seat belt retractor for retracting a seat belt so that the seat belt can be withdrawn, and a seat belt device equipped with the seat belt retractor. More specifically, the present invention relates to a seat belt retractor including an energy absorbing mechanism (hereinafter referred to as EA mechanism) for absorbing an impact energy of the seat belt on an occupant moving due to inertia in case of emergency such as a collision, in which a vehicle is significantly decelerated, and a seat belt device equipped with the seat belt retractor.
A conventional seat belt device is installed in a vehicle such as an automobile, and includes at least a seat belt retractor for retracting a seat belt, a seat belt capable of being withdrawn from the seat belt retractor and having an end connected to an auto body, a buckle fixed to the auto body, and a tongue slidably fitted to the seat belt and capable of engaging the buckle.
When the seat belt is not used, the seat belt is wound on a spool of the seat belt retractor. After an occupant is seated, the occupant withdraws the seat belt from the seat belt retractor for a predetermined length and engages the tongue with the buckle to wear the seat belt. When the occupant wears the seat belt, a portion of the seat belt between the tongue and the seat belt retractor is placed over a shoulder and chest as a shoulder belt, and a portion of the seat belt between the tongue and a connection with the auto body is placed round a waist as a lap belt.
In this state, in case of emergency, a locking mechanism is activated to lock the spool from rotating in an unwinding direction, thereby preventing the seat belt from being withdrawn. Accordingly, in the seat belt device, the shoulder belt restrains the shoulder and chest of the occupant, and the lap belt restrains the waist of the occupant, so that the occupant is not thrown forward for protection.
In such a seat belt retractor of the conventional seat belt device, when the seat belt restrains the occupant to protect the occupant in case of emergency such as a collision, the vehicle is significantly decelerated and the occupant is rushed forward due to large inertia. Consequently, a large load is applied on the seat belt, and the seat belt applies a large impact on the occupant. While the impact on the occupant does not cause a serious problem, it is desirable to absorb the impact energy to limit the impact force if possible.
To this end, there has been developed a seat belt retractor provided with a torsion bar for absorbing the impact energy to restrict the load applied to the seat belt in case of emergency. FIG. 16 is a vertical sectional view showing a seat belt retractor including such a torsion bar. The seat belt retractor includes a seat belt retractor 1; a U-shaped frame 2; a seat belt 3; a spool 4 rotatably supported between both sidewalls of the U-shaped frame 2 for winding the seat belt 3; deceleration sensing means 5 to be activated upon detecting a large deceleration in case of emergency; a locking mechanism 6 to be activated by the deceleration sensing means 5 for preventing the spool 4 from rotating at least in the direction of unwinding the seat belt; a torsion bar 7 inserted into the center of the spool 4 for connecting the spool 4 and the locking mechanism 6 to be rotatable; spring means 8 for constantly urging the spool 4 in the winding direction of the seat belt by the spring force of a spiral spring 9 via a bush 10; a pre-tensioner 11 to be activated in case of emergency for producing a belt winding torque; and a bush 12 for transmitting the belt winding torque from the pre-tensioner 11 to the spool 4.
The locking mechanism 6 includes a locking base 14 (corresponding to a locking member) supported on a first torque transmitting portion 17 of the torsion bar 7 to be rotatable therewith for holding a pawl 13 to be rotatable. The locking mechanism 6 further includes a locking gear 6a. The locking gear 6a rotates together with the torsion bar 7 in a normal state. In case of emergency, the locking gear 6a stops through an operation of the deceleration sensing means 5, so that a rotational difference relative to the torsion bar 7 is generated. Accordingly, the pawl 13 engages internal teeth 19 on a sidewall of the frame 2 to prevent the locking base 14, i.e. the spool 4, from rotating in the unwinding direction of the seat belt.
The torsion bar 7 is provided with a first torque transmitting portion 17 for engaging the locking base 14 so that the torsion bar 7 does not rotate relative to the locking base 14, and a second torque transmitting portion 18 for engaging the spool 4 so that the torsion bar 7 does not rotate relative to the spool 4. A relative rotation locking member 15 with a ring shape is disposed between the spool 4 and the shaft portion 14a of the locking base 14. The relative rotation locking member 15 has a female thread 15a on an inner peripheral surface thereof engaging a male thread 14c formed on the shaft portion 14a of the locking base 14. Accordingly, the relative rotation locking member 15 is screwed in an axial hole of the spool 4, so that the relative rotation locking member 15 does not rotate relative to the spool 4 and moves in an axial direction. When the spool 4 rotates in the unwinding direction of the seat belt relative to the locking base 14, the relative rotation locking member 15 rotates together with the spool 4 and moves to the right in FIG. 16.
With the spring force of the spring means 8, the spool 4 is urged constantly in the winding direction of the seat belt via the bush 10, the torsion bar 7, the second torque transmitting portion 18 of the torsion bar 7, and the bush 12. When the pre-tensioner 11 is activated, the belt winding torque produced in the pre-tensioner 11 is transmitted to the spool 4 via the bush 12, so that the spool 4 winds the seat belt for a predetermined length.
In the conventional seat belt retractor 1 with the configuration described above, when the seat belt is not used, the seat belt 3 is retracted completely with the urging force of the spring means 8. When the seat belt 3 is withdrawn in a normal speed for wearing, the spool 4 rotates in the unwinding direction of the seat belt, and the seat belt 3 is withdrawn smoothly. After a tongue (not shown) slidably fitted to the seat belt 3 is inserted into and engages a buckle (not shown), an excess portion of the seat belt 3 is wound on the spool 4 with the urging force of the spring means 8, so that the seat belt 3 is fitted to the occupant without inflicting a pressure.
In case of emergency, the belt winding torque produced by the pre-tensioner 11 is transmitted to the spool 4. The spool 4 quickly winds the seat belt 3 for a predetermined length to protect the occupant. At the same time, the deceleration sensing means 5 is activated by the large deceleration in the emergency, and the locking mechanism 6 is activated. By the operation of the deceleration sensing means 5, the lock gear 6a is prevented from rotating in the unwinding direction of the seat belt, and the pawl 13 of the locking mechanism 6 rotates and engages the internal teeth 19 on the sidewall of the frame 2. Accordingly, the locking base 14 is prevented from rotating in the unwinding direction of the seat belt, so that the torsion bar 7 is twisted and the spool 4 alone rotates in the unwinding direction of the seat belt relative to the locking base 14.
After that, the spool 4 rotates and the torsion bar 7 twists in the unwinding direction of the seat belt, thereby absorbing the impact energy on the occupant and restricting the load applied to the seat belt 3. The torsion bar 7 constitutes the EA mechanism, and the EA mechanism generates a counter load (hereinafter referred to as EA load) as shown in FIG. 4. The EA load generated by the torsion bar 7 increases gradually as a rotational stroke (degree) of the spool 4 relative to the locking base 14 increases, and then becomes a constant value.
When the spool 4 rotates in the unwinding direction of the seat belt relative to the locking base 14, the relative rotation locking member 15 moves axially in the right direction in FIG. 16. When the relative rotation locking member 15 reaches an end of the male thread, the relative rotation locking member 15 stops moving further to the right and is locked. The relative rotation locking member 15 stops the rotation relative to the locking base 14. The relative rotation locking member 15 may contact a side surface of a flange 14b of the locking base 14 to stop moving further to the right.
Accordingly, the spool 4 stops rotating relative to the locking base 14. That is, the rotation of the spool 4 in the unwinding direction of the seat belt is locked, and the seat belt 3 is prevented from being withdrawn. As a result, the seat belt 3 prevents the movement of the occupant caused by inertia, and protects the occupant.
In the seat belt retractor 1, when the seat belt is withdrawn suddenly, the locking base 14 of the locking mechanism 6 rotates in the unwinding direction of the seat belt relative to the locking gear 6a. The pawl 13 of the locking mechanism 6 engages the inner teeth 19 on the sidewall of the frame 2 to stop the locking base 14. Accordingly, the spool 4 is prevented from rotating in the unwinding direction via the torsion bar 7, so that the seat belt is not withdrawn.
In the seat belt retractor 1, only the torsion bar 7 generates the EA load to absorb the impact energy on the occupant. The EA load is set at a minimum and constant level for absorbing the impact energy so that the impact load on the occupant is made as small as possible. It is possible to absorb the impact energy on the occupant in an emergency using the torsion bar. However, it is desirable to absorb the impact energy on the occupant more effectively and properly.
For example, Japanese Patent Publication (Kokai) No. 2002-53007 has disclosed impact energy absorbing means disposed between a spool and a locking base and including a wire and an engaging pin engaging the wire. When the spool rotates relative to the locking base, the engaging pin forces the wire to deform through a rotation of the spool, thereby absorbing the impact energy.
In Japanese Patent Publication (Kokai) No. 2000-85527, a carrier is fixed to an end of a torsion rod so as to rotate together with the end. The carrier is connected to an end of band-shaped pulling means, and the band-shaped pulling means is inserted into a curved guide groove formed in a housing. When the carrier rotates relative to the housing, the guide groove forces the pulling means to deform through the rotation of the carrier, thereby absorbing the impact energy.
Japanese Patent No. 2875505 has disclosed another technique for absorbing the impact energy on the occupant. In the technique, just after a seat belt is locked, a predetermined resistance against unwinding is applied on a webbing to maintain a predetermined tension load of the webbing. The webbing is unwound for a predetermined length while maintaining the tension load, thereby absorbing the impact energy on the occupant.
In the technique disclosed in Japanese Patent No. 2875505, a shaft is disposed rotatably inside the spool winding the webbing. A locking mechanism is provided for locking the shaft so that the webbing is not unwound, and an energy absorbing member (EA plate) capable of deforming plastically is disposed between the spool and the shaft. In case of emergency, when the locking mechanism locks the shaft not to rotate, the webbing restrains the occupant moving forward due to inertia, and the webbing is pulled to rotate the spool relative to the shaft in the unwinding direction of the webbing. When the relative rotational force exceeds a certain value, the EA plate deforms plastically and wound around the shaft in the unwinding direction of the webbing, thereby absorbing the impact energy through the plastic deformation. Accordingly, in a state that the locking mechanism locks the spool, the spool still rotates and the webbing is unwound with a certain tension, thereby reducing the force between the webbing and the occupant.
In the energy absorbing means disclosed in Japanese Patent Publication (Kokai) No. 2002-53007, it is necessary that the wire engages all of three engaging pins while winding. Further, while the wire engages the three engaging pins, an end of the wire needs to be inserted into a hole formed in the locking base. Accordingly, the energy absorbing means has a complex structure and takes a lot of time and labor to assemble. Furthermore, in order to stably obtain a desired energy absorbing effect, it is necessary to provide the three engaging pins at predetermined places on the spool, thereby making the energy absorbing means expensive.
In the energy absorbing means disclosed in Japanese Patent Publication (Kokai) No. 2000-85527, the cylindrical portion deforms plastically toward inside for absorbing the impact energy. However, it is difficult to deform the cylindrical portion plastically toward the inside evenly, so that it is difficult to stably obtain the desired energy absorbing effect. In addition, the energy absorbing means is composed of the cylindrical portion and a flange portion, and it is necessary to form a cut-off portion in the cylindrical portion. Accordingly the energy absorbing means has a complex structure and difficult to make, thereby increasing cost. In addition, the cylindrical portion makes the retractor large in an axial direction.
Generally, a vehicle generates a different impact upon collision depending on a structure thereof. Therefore, in order to protect the occupant sufficiently, according to a structure of the vehicle, it is necessary to optimize the energy absorption characteristic such as a load for activating the energy absorbing mechanism to operate (energy absorption load: tension of the webbing when the energy absorption starts) and an amount of deformation upon the impact absorption (length of the unwound webbing). Consequently, in an entire structure of the retractor, it is required to optimize and design the energy absorption characteristic flexibly and freely.
In the technique disclosed in Japanese Patent No. 2875505, it is not considered to adjust the EA plate to optimize the impact energy, and no structure and technique have been disclosed. Accordingly, it is difficult to optimize the energy absorption characteristic.
In view of the problems described above, the present invention has been made, and an object of the present invention is to provide a seat belt retractor with a simple structure and low cost, and it is possible to adjust the EA load through deformation of an energy absorbing member.
It is another object of the present invention to provide a seat belt device provided with a seat belt retractor for effectively absorbing the impact energy on the occupant, and for restraining and protecting the occupant appropriately in case of emergency.
It is a further object of the present invention to provide a seat belt retractor capable of optimizing the energy absorption characteristic easily.
Further objects and advantages of the invention will be apparent from the following description of the invention.